The claustrum is a brain structure that receives inputs from nearly all of the neocortex and, in return, coordinates the activity of many brain regions. How the information that is collected in the claustrum is transmitted back to individual cortical areas is still unclear. Kitanishi and Matsuo studied the function of selected claustro-cortical projections in mice. A group of neurons in the anterior claustrum projects extensively into the medial entorhinal cortex, a brain region that plays a key role in spatial and contextual information processing. This circuit was activated by novel context exposure, and silencing it selectively during fear conditioning suppressed memory retrieval later. This pathway thus influences medial entorhinal cortex function precisely without affecting broad cortical activity.